The present application claims priority from European Patent Application No. 01302113.4, filed Mar. 8, 2001.
This invention relates to valve systems for fluid delivery systems.
A generic fluid delivery system may comprise a reservoir containing fluid to be delivered, a feed pump to maintain delivery pressure through delivery pipes, a control valve and a target tank to be filled.
One example of such a system has a control valve used to control the delivery of a gas, such as CO2, from the reservoir to the tank whilst preventing back-flow of gas into the delivery reservoir. This back-flow could cause potentially contaminating substances to be transmitted from the tank to the delivery reservoir, in turn, this could cause pollution of the xe2x80x9cpurexe2x80x9d source gas in the reservoir, potentially contaminating future delivery sites.
Prior art valves in known gas delivery systems contain a single check valve and failure of this valve has been known to lead to such contamination of the delivery reservoir. As such valve systems are incorporated into mobile delivery systems which tour various industrial sites, valve failure and subsequent contamination has been known to occur at a heavy industrial site, where contamination is not a significant issue, this contamination has then been supplied to an alternative site where the gas is used in products for human consumption, causing severe safety problems.
Alternative prior art valve systems have incorporated two check valves rather than one, to allow for redundancy should one fail. In such systems, if the valve adjacent to the outlet fails, the space between the valves may be vented. However, when this cavity is vented, the check valve adjacent to the inlet is opened due to the pressure difference that then occurs. As a result of this opening valve constant venting of the delivery reservoir will occur and inventory will be lost. Whilst prevention of contamination of the delivery reservoir may be achieved, if resumption of a suitable pressure difference is not resumed rapidly not only may a significant portion of the inventory be lost to atmosphere but the venting jet may cause disruption or a safety hazard in the vicinity of the equipment.
It is an aim of the present invention to overcome the contamination problems of the earlier prior art without introducing a constant venting condition.
According to the present invention there is provided a valve system, for controlling the dispensing, in use, of a fluid, the valve system comprising first and second valve members defining a cavity therebetween, the first valve member having a closed position and an open position and providing a seal between an inlet of the valve system and the cavity whilst in the closed position and allowing passage of fluid from the inlet to the cavity whilst in the open position and the second valve member having a closed position and an open position and providing a seal between the cavity and an outlet of the valve system whilst in the closed position and allowing passage of the fluid from the cavity to the outlet whilst in the open position, thereby controlling the passage of fluid through the valve system, the valve system further comprising means for controlling venting of the cavity dependant upon the relative values of the valve system inlet and outlet pressures.
The valve members may be automatically returned to their closed positions by biassing means, these biassing means may be provided by springs. The venting of the internal cavity may be controlled by use of a diaphragm valve.